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Gage Blocks - Jo Blocks.


Gage blocks are small pieces of steel that have been ground and lapped to very fine resolution of accuracy. 

These blocks were originally created by Carl Edvard Johansson, Swedish born in 1864. He devised a method of using his wife's sewing machine to lap 2 surfaces very carefully to produce not only a size tolerance required for the blocks to be used as inspection and set up instruments but also so both surfaces are flat and parallel to each other.


His wife's modified sewing machine, the picture has more of a description.
Thanks to Peter Short from New Zealand for the scan.
From the book:
C.E. Johansson 1864-1943; The Master of Measurement

While working for Carl Gustav as a armorer inspector, inspecting the finished rifles, Sweden went to the M94 Mauser rifle. When he went to inspect how the Germans at the Mauser plant inspected the rifles and how they gaged the accuracy of the part he was not pleased. When he returned he conceived the notion of precision blocks to aid in the inspection and manufacturing of the rifles to be done at the Carl Gustav Arsenal.

Oldest known gage block set in the world. 49 Gage blocks produced before the turn of the last century!
Thanks to Peter Short from New Zealand for the scan.
From the book:
C.E. Johansson 1864-1943; The Master of Measurement

He received Patent number 17017 for "Gauge Block Sets for Precision Measurement" in 1901 from the Swedish government. He formed CE Johansson AB in 1911 and CE Johansson Lic. in 1918. In 1923 Ford Motor Co bought out his American company and hired him to produce his gage block sets for Ford. Due to this, many of the older original sets of blocks are labeled "Ford Motor Corp", "CE Johansson" and/or "CEJ".

Oldest surviving gage block set in the US. Originally purchased by the Morse Twist Drill Co,
then traded back to Ford in 1930 for a new set. Thanks to Peter S from New Zealand for the scans!
From the book
Henry's Attic by Ford R. Bryan.

When using gage blocks. We generally must use multiple gage blocks at a time. This is so we can get our 4 digits of accuracy with a imperial inch set or 2 digits of accuracy with a metric millimeter set. We have many uses in the shop for them. However its only limited by the users ability to understand and realize what kind of a useful tool is a gage block set to a machinist or quality control inspector in the machine shop. 

Now that we have talked about some of the theory behind the use of gage blocks, we must talk about the accuracy of current gage block sets. Gage block tolerances are controlled by ANSI B89.1.9:2002 "Gage Blocks".

The following tolerance levels are defined.

Imperial Inch Gage Blocks Tolerances:


Laboratory Master Grade

Grade 00 or AA

Grade 0 or A1

Size

Length Variation

Flatness

Size

Length Variation

Flatness

Size

Length Variation

Flatness

Thru .050”

+/-1.2

1.2

1.2

+/-4.0

2

2

+/-6.0

4

4

Thru .400”

+/-1.2

1.2

1.2

+/-3.0

2

2

+/-5.0

4

4

Thru 1”

+/-1.2

1.2

1.2

+/-3.0

2

2

+/-6.0

4

4

Thru 2”

+/-2.0

1.2

1.2

+/-4.0

2

2

+/-8.0

4

4

Thru 3”

+/-3.0

1.2

1.2

+/-5.0

3

Rect. 2/Sq. 3

+/-10.0

4

4

Thru 4”

+/-4.0

1.2

1.2

+/-6.0

3

Rect. 2/Sq. 3

+/-12.0

5

4

Thru 5”




+/-8.0

3

Rect. 2/Sq. 3

+/-16.0

5

4

Thru 6”




+/-8.0

3

Rect. 2/Sq. 3

+/-16.0

5

4

Thru 7”




+/-10.0

4

4

+/-20.0

6

6

Thru 8”




+/-10.0

4

4

+/-20.0

6

6

Thru 10”




+/-12.0

4

4

+/-24.0

6

6

Thru 12”




+/-14.0

4

4

+/-28.0

7

6

Thru 16”




+/-18.0

5

4

+/-36.0

8

6

Thru 20”




+/-20.0

6

4

+/-44.0

10

6


One thing to remember with this above table is that the tolerances are all in micro inches. Which one micro inch is actually .000001". If you look at your micrometer you will notice it only measures up to .0001" so we are over 10 times more accurate with gage blocks then we are with the measuring ability of the micrometer.

Metric Gage Block Tolerances:


Laboratory Master Grade

Grade 00 or AA

Grade 0 or A1

Size

Length Variation

Flatness

Size

Length Variation

Flatness

Size

Length Variation

Flatness

Thru 0.5mm

+/-.03

0.03

0.03

+/-10

0.05

0.05

+/-.14

0.1

0.1

Thru 10mm

+/-.03

0.03

0.03

+/-.07

0.05

0.05

+/-.12

0.1

0.1

Thru 25mm

+/-.04

0.03

0.03

+/-.07

0.05

0.05

+/-.14

0.1

0.1

Thru 50mm

+/-.05

0.03

0.03

+/-.10

0.06

0.05

+/-.20

0.1

0.1

Thru 75mm

+/-.08

0.03

0.03

+/-.12

0.07

Rect .05/Sq .07

+/-.25

0.12

0.1

Thru 100mm

+/-.10

0.03

0.03

+/-.15

0.07

Rect .05/Sq .07

+/-.30

0.12

0.1

Thru 125mm




+/-.20

0.08

Rect .05/Sq .07

+/-.40

0.14

0.1

Thru 150mm




+/-.20

0.08

Rect .05/Sq .07

+/-.40

0.14

0.1

Thru 175mm




+/-.25

0.09

0.1

+/-.50

0.16

0.15

Thru 200mm




+/-.25

0.09

0.1

+/-.50

0.16

0.15

Thru 250mm




+/-.30

0.1

0.1

+/-.60

0.16

0.15

Thru 300mm




+/-.35

0.1

0.1

+/-.70

0.18

0.15

Thru 400mm




+/-.45

0.12

0.1

+/-.90

0.2

0.15

Thru 500mm




+/-.50

0.14

0.1

+/-1.1

0.25

0.15


Now in this case however the gage block base tolerance dimension is actually 0.001mm.

Tolerances for gage blocks can be compared:

  • Starrett Grade LM = GGG-G-15C Grade 0.5 = B89.1.9 Grade for this is not specified.
  • Starrett Grade AA = GGG-G-15C Grade 1 = B89.1.9 Grade 00. This Grade exceeds the DIN (German), ISO and BS (British) K Grade.
  • Starrett Grade A1 = GGG-G-15C Grade 2 = B89.1.9 Grade 0.
  • Starrett Grade A = GGG-G-15C Grade 3 = B89.1.9 Grade AS1.

The following few pages hopefully will make the use of gage blocks and their importance in the shop well understood to even someone new to machining. As well below is the Mil GGG-C-15C specifications for Gage Blocks. Which is referenced by Starrett and other Gage block manufacturers. And is referenced above by me as well.

Dimitrios Simitas

Ċ
Dimitrios Simitas,
Feb 27, 2010, 10:40 PM
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